Message-ID: <f2fa741f5f818650b071eca23be16fb2bdb3c759.camel@sipsolutions.net>
Subject: Re: [PATCH] mac80211: allow scans on radar channels, unless there
 is CAC or CSA
From:   Johannes Berg <johannes@sipsolutions.net>
To:     Simon Wunderlich <sw@simonwunderlich.de>
Cc:     linux-wireless@vger.kernel.org, Eliad Peller <eliad@wizery.com>,
        mathias.kretschmer@fit.fraunhofer.de
Date:   Fri, 29 Mar 2019 11:35:14 +0100
In-Reply-To: <2969898.mUHQksrBSp@prime>
References: <20180918141633.10282-1-sw@simonwunderlich.de>
         <1537435276.3874.14.camel@sipsolutions.net> <2969898.mUHQksrBSp@prime>
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On Thu, 2018-09-20 at 12:27 +0200, Simon Wunderlich wrote:
> On Thursday, September 20, 2018 11:21:16 AM CEST Johannes Berg wrote:
> > On Tue, 2018-09-18 at 16:16 +0200, Simon Wunderlich wrote:
> > > Operating on a DFS channel doesn't mean we can't leave it for a short
> > > time - actually, some features like off-channel CAC work by leaving the
> > > operation channel to check other channels for availability (although
> > > off-channel CAC isn't implemented in mac80211). In our case, we want to
> > > use mesh while doing background surveys on other channels from time to
> > > time.
> > 
> > Actually ... as far as I can tell it *does* mean that, at least
> > currently for FCC.
> 
> 
> Mhm. I remember you said that before. But I can't find references for it. I 
> checked the FCC 15.407 document [1] but couldn't find anything in favor or 
> against that. Same for the measurement procedures [2]. I also couldn't find 
> off-channel CAC in FCC, which I used for my argument in ETSI:
> 
> In ETSI 301 893 [3] they talk about non-continuous checks for off-channel CAC 
> (in 4.2.6.2.3, second paragraph) and continuous period for CAC (4.2.6.2.2.2, 
> first paragraph). Continuity is not mentioned for in-service monitoring 
> (4.2.6.2.4), but off-channel CAC could only work when continuity is not 
> required.
> 
> I'd appreciate if you (or someone else) can point me to where it's stated that 
> we can't leave the channel for the a short time. I'm assuming that we are back 
> fast enough to ensure the required detection probability.

I still don't have a document, but we spoke about it at the wireless
workshop and Jouni agrees that this is an absolute no-go for FCC, while
allowed for ETSI.

I guess you can make it depend on the radar domain information.

johannes